Zoom lens and photographing apparatus

ABSTRACT

A zoom lens and a photographing apparatus including the same. The zoom lens includes a first lens group having a positive refractive power, a second lens group having a negative refractive power, and an additional lens grouping having a positive refractive power, which are sequentially arranged from an object side, wherein the additional lens grouping comprises a third lens group having a positive refractive power.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims the benefit of Japanese Patent Application No.2009-286705, filed on Dec. 17, 2009, in the Japanese Patent Office, andKorean Patent Application No. 10-2010-0119789, filed on Nov. 29, 2010,the disclosures of which are incorporated herein in their entirety byreference.

BACKGROUND

The invention relates to a zoom lens and a photographing apparatus.

Focusing mechanisms of zoom lenses at a minimum distance are classifiedinto focusing by a first lens group that is closest to an object sideand focusing by a lens group other than the first lens group.

A zoom lens focused by the first lens group can be easily designed dueto its simple structure. In particular, in a zoom lens including apositive lens having a wide angle region which is disposed at the frontof the first lens group, the diameter of the zoom lens may be increased.A zoom lens focused by a lens group other than the first lens groupwhich overcomes drawbacks of the zoom lens focused by the first lensgroup is focused by a negative second lens group disposed at an imageside of the first lens group and includes a positive lens disposed atthe front of the second lens group, and thus is suitable for high zoommagnification.

However, in the zoom lens in which the focusing is performed by thenegative second lens group and the positive lens is disposed at thefront of the negative second lens group, the second lens group generallyplays a critical role in zooming, and thus the number of lenses mayincrease and the weight of the zoom lens may also increase. Thus, such azoom lens is not suitable for controlling a minute shift of the secondlens group forward or backward, in particular, auto-focusing control bybokeh sensing of an imaging device.

It is also known that, a zoom lens including a positive first lensgroup, a negative second lens group, and a positive third lens groupwhich are sequentially arranged from an object side may be focused bythe third lens group.

However, since the number of lenses increases when the focusing isperformed by the third lens group, a minute control of the third lensgroup, for example a minute shift of the third lens group forward orbackward, is not easy.

SUMMARY

Embodiments of the invention provide a zoom lens having high zoommagnification, excellent optical performance from the wide angleposition to the telephoto position, and excellent focusing performanceat the minimum distance, and a photographing apparatus including thezoom lens.

According to an embodiment of the invention, there is provided a zoomlens including: a first lens group having a positive refractive power, asecond lens group having a negative refractive power, and a followinglens group having a positive refractive power, which are sequentiallyarranged from an object side, wherein the following lens group comprisesa third lens group having a positive refractive power, wherein when aneffective focal length of the third lens group refers to f₃[mm], and aneffective focal length of the following lens group at the telephotoposition refers to f_(rt)[mm], and an effective focal length of thesecond lens group refers to f₂[mm], the zoom lens may satisfy thefollowing formulae.

Formulae0.1<f ₃ /f _(rt)<2.0,1.5<|f ₃ /f ₂<4.0

A distance between the first lens group and the second lens group mayincrease and a distance between the second lens group and the third lensgroup may decrease during zooming from the wide angle position to thetelephoto position.

The third lens group may be shifted towards an image side to perform afocusing at a minimum distance.

The third lens group may include one piece of positive lens.

When a transverse magnification of the third lens group when focused onan object at infinite distance at the telephoto position refers toβ_(3t), and a transverse magnification of a lens group that is disposedcloser to the image side than the third lens group and focused on anobject at infinite distance at the telephoto position refers to β_(xt),the zoom lens may satisfy the following formula.

Formula|(1−β_(3t) ²)×β_(xt) ²|>2.0

When a transverse magnification of the third lens group when focused onan object at infinite distance at the wide angle position refers toβ_(3w), and a transverse magnification of a lens group that is disposedcloser to the image side than the third lens group and focused on anobject at infinite distance at the telephoto position refers to β_(xw),the zoom lens may satisfy the following formula.

Formula{(1−β_(3w) ²)×β_(xw) ²}/{(1−β_(3t) ²)×β_(xt) ²}>0

An effective focal length of the first lens group refers to f₁[mm], aneffective focal length of the second lens group refers to f₂[mm], atotal focal length of the zoom lens at the wide angle position refers tof_(w)[mm], and a total focal length of the zoom lens at the telephotoposition refers to f_(t)[mm], the zoom lens may satisfy the followingformulae.

Formulae1.0<|f ₁/(f _(w) ×f _(t))^(1/2)|<5.0,0.1<|f ₂/(f _(w) ×f _(t))^(1/2)|<1.0,0.5<|f _(rt)/(f _(w) ×f _(t))^(1/2)|<3.0,

The following lens group may further include a fourth lens group and afifth lens group which are sequentially disposed between the third lensgroup and the image side, wherein the distance between the fourth lensgroup and the fifth lens group may vary during zooming.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the invention will becomemore apparent by describing in detail exemplary embodiments thereof withreference to the attached drawings in which:

FIG. 1 shows a zoom lens according to an embodiment of the invention;

FIG. 2 shows a zoom lens according to Embodiment 1;

FIG. 3 shows an aberration diagram of the zoom lens according toEmbodiment 1 when focused on an object at infinite distance at the wideangle position;

FIG. 4 shows an aberration diagram of the zoom lens according toEmbodiment 1 when focused on an object at a minimum distance (0.45 m) atthe wide angle position;

FIG. 5 shows an aberration diagram of the zoom lens according toEmbodiment 1 when focused on an object at infinite distance at themiddle position;

FIG. 6 shows an aberration diagram of the zoom lens according toEmbodiment 1 when focused on an object at a minimum distance (0.45 m) atthe middle position;

FIG. 7 shows an aberration diagram of the zoom lens according toEmbodiment 1 when focused on an object at infinite distance at thetelephoto position;

FIG. 8 shows an aberration diagram of the zoom lens according toEmbodiment 1 when focused on an object at a minimum distance (0.45 m) atthe telephoto position;

FIG. 9 shows a zoom lens according to Embodiment 2;

FIG. 10 shows an aberration diagram of the zoom lens according toEmbodiment 2 when focused on an object at infinite distance at the wideangle position;

FIG. 11 shows an aberration diagram of the zoom lens according toEmbodiment 2 when focused on an object at a minimum distance (0.45 m) atthe wide angle position;

FIG. 12 shows an aberration diagram of the zoom lens according toEmbodiment 2 when focused on an object at infinite distance at themiddle position;

FIG. 13 shows an aberration diagram of the zoom lens according toEmbodiment 2 when focused on an object at a minimum distance (0.45 m) atthe middle position;

FIG. 14 shows an aberration diagram of the zoom lens according toEmbodiment 2 when focused on an object at infinite distance at thetelephoto position;

FIG. 15 shows an aberration diagram of the zoom lens according toEmbodiment 2 when focused on an object at a minimum distance (0.45 m) atthe telephoto position;

FIG. 16 shows a zoom lens according to Embodiment 3;

FIG. 17 shows an aberration diagram of the zoom lens according toEmbodiment 3 when focused on an object at infinite distance at the wideangle position;

FIG. 18 shows an aberration diagram of the zoom lens according toEmbodiment 3 when focused on an object at a minimum distance (0.45 m) atthe wide angle position;

FIG. 19 shows an aberration diagram of the zoom lens according toEmbodiment 3 when focused on an object at infinite distance at themiddle position;

FIG. 20 shows an aberration diagram of the zoom lens according toEmbodiment 3 when focused on an object at a minimum distance (0.45 m) atthe middle position;

FIG. 21 shows an aberration diagram of the zoom lens according toEmbodiment 3 when focused on an object at infinite distance at thetelephoto position;

FIG. 22 shows an aberration diagram of the zoom lens according toEmbodiment 3 when focused on an object at a minimum distance (0.45 m) atthe telephoto position;

FIG. 23 shows a zoom lens according to Embodiment 4;

FIG. 24 shows an aberration diagram of the zoom lens according toEmbodiment 4 when focused on an object at infinite distance at the wideangle position;

FIG. 25 shows an aberration diagram of the zoom lens according toEmbodiment 4 when focused on an object at a minimum distance (0.45 m) atthe wide angle position;

FIG. 26 shows an aberration diagram of the zoom lens according toEmbodiment 4 when focused on an object at infinite distance at themiddle position;

FIG. 27 shows an aberration diagram of the zoom lens according toEmbodiment 4 when focused on an object at a minimum distance (0.45 m) atthe middle position;

FIG. 28 shows an aberration diagram of the zoom lens according toEmbodiment 4 when focused on an object at infinite distance at thetelephoto position; and

FIG. 29 shows an aberration diagram of the zoom lens according toEmbodiment 4 when focused on an object at a minimum distance (0.45 m) atthe telephoto position.

DETAILED DESCRIPTION

Hereinafter, a zoom lens and a photographing apparatus according to theinvention will now be described more fully with reference to theaccompanying drawings, in which exemplary embodiments of the inventionis shown.

Lens data, etc., which will be described hereinafter are exemplary data,are not limited thereto and may be modified in various ways not tochange the scope of the invention.

A zoom lens according to an embodiment of the invention may be used as aphotographing optical system of a photographing apparatus such as awatching camera, a digital video camera, and a digital still camera.Referring to FIG. 1, for example, the zoom lens may include a first lensgroup L1 having a positive refractive power, a second lens group L2having a negative refractive power, and the following lens group Lrhaving a positive refractive power, which are sequentially arranged froman object side O. The following lens group Lr may include a third lensgroup L3 having a positive refractive power, a fourth lens group L4having a negative refractive power, and a fifth lens group L5 having apositive refractive power. FIG. 1 shows arrangements of lenses at thewide angle position, the middle position, and the telephoto position ofthe zoom lens.

The first lens group L1 may include a negative meniscus lens 1 with aconvex surface towards the object side O and a positive lens 2. Themeniscus lens 1 and the positive lens 2 may form a doublet lens. Thesecond lens group L2 may include a negative meniscus lens 3 with aconvex surface towards the object side O, a biconcave lens 4, and apositive lens 5 with a convex surface towards the object side O. Thethird lens group L3 may include a biconvex lens 6. The fourth lens groupL4 may include a doublet lens having a positive lens 7 and a negativelens 8 and a doublet lens having a positive lens 9 and a negative lens10. The fifth lens group L5 may include a positive lens 11 and anegative lens 12. In addition, a stop S is disposed between the thirdlens group L3 and the fourth lens group L4, and an optical filter suchas a low pass filter (LPF) is disposed between the fifth lens group L5and an image plane IP.

In the zoom lens, each of the first to fifth lens groups L1 to L5 maymove towards the object side O during zooming from the wide angleposition to the telephoto position such that an axial distance betweenthe first lens group L1 and the second lens group L2 increases and anaxial distance between the second lens group L2 and the third lens groupL3 decreases, as shown in FIG. 1. In addition, the stop S may beintegrally shifted with the fourth lens group L4 during zooming. Inaddition, as shown with an arrow F of FIG. 1, the third lens group L3 isshifted towards the image plane side I to perform a focusing at theminimum distance. The doublet lens including the positive lens 9 and thenegative lens 10 of the fourth lens group L4 is shifted in a directionperpendicular to the optical axis to correct image shake caused by handshaking.

In a photographing apparatus, light incident from the object side O ofthe zoom lens is formed on an image plane IP. For example, an image isformed on an image surface of an imaging device (photoelectricconversion device such as a charge coupled device (CCD) or acomplementary metal-oxide semiconductor device (CMOS) sensor. Thephotographing apparatus photoelectrically converts the light received bythe imaging device into an electrical signal and outputs the electricalsignal, and then forms a digital image corresponding to an image of asubject and records the digital image in a recording medium such as ahard disk drive (HDD), a memory card, an optical disk, and a magnetictape. If the photographing apparatus is a film camera, the image planeIP is a film surface.

When an effective focal length of the third lens group L3 refers tof₃[mm], and an effective focal length of the following lens group Lr(third to fifth lens groups L3 to L5) at the telephoto position refersto f_(rt)[mm], and an effective focal length of the second lens group L2refers to f₂[mm], the zoom lens according to the current embodiment maysatisfy Formulae 1 and 2 below.0.1<f ₃ /f _(rt)<2.0  Formula 11.5<|f ₃ /f ₂|<4.0  Formula 2

In order to obtain excellent optical performance from the wide angleposition to the telephoto position, the arrangement of the refractivepower of the third lens group L3 (focus lens group) needs to beoptimized. Formulae 1 and 2 limit the arrangement of the refractivepower of the third lens group. If the f₃/f_(rt) is less than the lowerlimit of Formula 1, a spherical aberration occurring at the third lensgroup L3 increases so that variation of the spherical aberration causedby focusing cannot be reduced. If the f₃/f_(rt) is greater than theupper limit of Formula 1, a moving distance for focusing cannot becontrolled at the telephoto position, and thus the size and the weightof the zoom lens may increase. In addition, in order to correct thespherical aberration of the third lens group L3 when the f₃/f_(rt) isless than the lower limit of Formula 1, the number of lens of the thirdlens group L3 increases to increase the weight of the third lens groupL3.

If the |f₃/f₂| is less than the lower limit of Formula 2, a highmagnification may not be obtained. If the |f₃/f₂| is greater than theupper limit of Formula 2, the refractive power of the second lens groupL2 increases so that a Petzval sum cannot be reduced, and a fieldcurvature or astigmatism may increase.

The zoom lens according to the current embodiment may satisfy Formulae 3and 4 below.0.2<f ₃ /f _(rt)<1.5  Formula 32.0<|f ₃ /f ₂|<3.2  Formula 4

The zoom lens according to the current embodiment may satisfy Formula 5below.0.4<f ₃ /f _(rt)<1.5  Formula 5

In the zoom lens according to the current embodiment, the third lensgroup L3 may include one piece of positive lens in order to reduce theweight of the third lens group L3. Accordingly, the third lens group L3may be easily shifted forward and backward, and the zoom lens may besuitable for, so called, mountain climbing auto-focusing control bybokeh sensing of a solid imaging device.

If a transverse magnification of the third lens group L3 when focused onan object at infinite distance at the telephoto position refers toβ_(3t), and a transverse magnification of the fourth and fifth lensgroups L4 and L5 which are disposed closer to the image side I than thethird lens group L3 and focused on an object at infinite distance at thetelephoto position refers to β_(xt), the zoom lens according to thecurrent embodiment may satisfy Formula 6 below.|(1β_(3t) ²)×β_(xt) ²|>2.0  Formula 6

When the zoom lens satisfies Formula 6, a moving distance for focusingat the telephoto position may be reduced.

The zoom lens may satisfy Formula 7 below.|(1−β_(3t) ²)×β_(xt) ²|>3.0  Formula 7

The zoom lens may satisfy Formula 8 below.5.0>|(1−β_(3t) ²)×β_(xt) ²|  Formula 8

When the zoom lens satisfies Formula 8, focusing at the telephotoposition may not be too sensitive, and thus stop precision of the thirdlens group L3 may be optimized to simplify a focusing device.

If a transverse magnification of the third lens group L3 when focused onan object at infinite distance at the wide angle position refers toβ_(3w), and a transverse magnification of the fourth and fifth lensgroups L4 and L5 which are disposed closer to the image side I than thethird lens group L3 and focused on an object at infinite distance at thetelephoto position refers to β_(xw), the zoom lens according to thecurrent embodiment may satisfy Formula 9 below.{(1−β_(3w) ²)×β_(xw) ²}/{(1−β_(3t) ²)×β_(xt) ²}>0  Formula 9

When the zoom lens satisfies Formula 9, the third lens group L3 isshifted in the same direction at the wide angle position and thetelephoto position when focused from the infinite distance to theminimum distance at the telephoto position, and thus the shift of thethird lens group L3 may be easily controlled.

The zoom lens may satisfy Formula 10 below.{(1−β_(3w) ²)×β_(xw) ²}/{(1−β_(3t) ²)×β_(xt) ²}>0  Formula 10

When an effective focal length of the first lens group L1 refers tof₁[mm], an effective focal length of the second lens group L2 refers tof₂[mm], an effective focal length of the zoom lens at the wide angleposition refers to f_(w)[mm], and an effective focal length of the zoomlens at the telephoto position refers to f_(t)[mm], the zoom lensaccording to the current embodiment may satisfy Formulae 11, 12, and 13below1.0<|f ₁/(f _(w) ×f _(t))^(1/2)|<5.0  Formula 110.1<|f ₂/(f _(w) ×f _(t))^(1/2)|<1.0  Formula 120.5<|f _(rt)/(f _(w) ×f _(t))^(1/2)|<3.0  Formula 13

When the zoom lens satisfies Formula 11, the spherical aberration may beeasily corrected. When the zoom lens satisfies Formula 12, a desiredzoom magnification may be easily obtained. In addition, when the zoomlens satisfies Formula 13, a desired back focal length may be easilyobtained.

The zoom lens according to the current embodiment may satisfy Formulae14, 15 and 16 below.1.3<|f ₁/(f _(w) ×f _(t))^(1/2)|<4.0  Formula 140.18<|f ₂/(f _(w) ×f _(t))^(1/2)|<0.7  Formula 151.0<|f _(rt)/(f _(w) ×f _(t))^(1/2)|<2.5  Formula 16

The zoom lens according to the current embodiment may satisfy Formulae17, 18 and 19 below.2.5<|f ₁/(f _(w) ×f _(t))^(1/2)|<4.0  Formula 170.35<|f ₂/(f _(w) ×f _(t))^(1/2)|<0.7  Formula 181.1<|f _(rt)/(f _(w) ×f _(t))^(1/2)|<1.8  Formula 19

In the zoom lens according to the current embodiment, the fourth lensgroup L4 and the fifth lens group L5 are sequentially disposed betweenthe third lens group L3 and the image side. During zooming, the distancebetween the fourth lens group L4 and the fifth lens group L5 may vary.Accordingly, in the following lens group L3 having the positiverefractive power, variation of the image plane according to the zoomingmay be easily corrected.

In addition, when the third lens group L3 includes an aspheric surfacehaving a positive refractive power that decreases as farther from theoptical axis, variation of the spherical aberration according tofocusing may be reduced.

The zoom lens according to the current embodiment may have high zoommagnification, excellent optical performance from the wide angleposition to the telephoto position, and excellent focusing performanceat the minimum distance. In addition, since the third lens group L3 maybe simplified and the weight thereof may be reduced, a minute shift ofthe third lens group L3 forward and backward may be easily performed.Accordingly, the zoom lens according to the current embodiment may besuitably used for the mountain climbing auto-focusing control by bokehsensing of the solid imaging device. For example, a small photographingapparatus that is suitable for a lens exchangeable lens digital stillcamera, or the like, and has high optical performance may be provided.

However, the invention is not limited thereto and may be modified invarious ways not to change the scope of the invention.

The following lens group Lr is not limited to those illustrated in FIG.1, and the number of the lens group and the constitution and arrangementof lenses may vary. The design of the zoom lens may vary. For example,the distance between two doublet lenses of the fourth lens L4 may beincreased so that the zoom lens has 6 lens groups during zooming fromthe wide angle position the telephoto position.

Hereinafter, the design data of the zoom lens according to an embodimentwill be described. However, the invention is not limited to thefollowing embodiments and may be modified in various ways not to changethe scope of the invention.

Hereinafter, a surface number Si, where i is a natural number, is thenumber of lens surface that is sequentially increased from a first lenssurface of a lens that is closest to the object side O towards the imageside. R is a curvature radius [mm] of the lens surface corresponding toeach surface number Si. D is an axial distance [mm] between the i^(th)lens surface and (i+1)^(th) lens surface from the object side O and D1to D5 (when varied) are axial distances [mm] therebetween at the wideangle position (f=18.55), at the middle position (f=28.0), and at thetelephoto position (f=53.4). In addition, Nd is a refractive index ofeach lens, and Vd is an Abbe's number of each lens. In addition, movingdistances of the third lens group L3 for focusing at the minimumdistance (0.45 m) at the wide angle position (f=18.55), at the middleposition (f=28.0), and at the telephoto position (f=53.4) are shown.Also, the unit of a focal length is mm.

Meanwhile, the aspheric surface used in the zoom lens may be obtained bythe Formula 20 below.

$\begin{matrix}{Z = {\frac{{Ch}^{2}}{1 + \sqrt{1 - {\left( {1 + K} \right)C^{2}h^{2}}}} + {\sum\limits_{i = 2}^{5}\;{A_{2i}h^{2\; i}}}}} & {{Formula}\mspace{14mu} 20}\end{matrix}$

Here, an optical axis is referred to as an x-axis. x indicates distancefrom the vertex of a lens along the optical axis, h indicates thedistance in the direction perpendicular to the optical axis direction, Kindicates a conic constant, A_(2i) indicates aspheric coefficients, andC indicates the inverse of radius of curvature (R) at the vertex of thelens.

Embodiment 1

FIG. 2 shows a zoom lens designed based on data of Embodiment 1. Thezoom lens shown in FIG. 2 has the same constitution as the zoom lensshown in FIG. 1, and lens data of the zoom lens is listed in Table 1below.

TABLE 1 Lens surface R D nd vd S1 52.409 2.00 1.84666 23.78 S2 35.3376.50 1.69680 55.46 S3 312.400 D1 S4 79.275 1.25 1.71300 53.94 S5 10.9467.10 S6 −61.407 2.10 1.69680 55.46 S7 23.884 0.27 S8 18.000 3.80 1.8051825.46 S9 63.286 D2 S10 37.784 2.00 1.60311 60.69 S11 −45.794 D3 S12 stop0.10 S13 13.511 3.35 1.48749 70.44 S14 −37.908 0.70 1.84666 23.78 S1595.533 3.84 S16 −306.745 1.75 1.70154 41.15 S17 −18.178 0.55 1.6385455.45 S18 38.555 D4 S19 30.717 3.25 1.58313 59.46 S20 −27.831 1.51 S21−23.230 1.80 1.80611 40.73 S22 −84.987 D5 S23 plane 2.24 1.51633 64.14S24 plane 0.10

Variable distances during zooming from the wide angle position to thetelephoto position are shown in Table 2 below.

TABLE 2 Wide angle Variable position Middle Telephoto distance (f =18.55) position (f = 28.0) position (f = 53.4) D1 0.861 9.606 23.813 D215.335 9.047 2.380 D3 4.196 4.585 5.838 D4 4.530 3.323 1.930 D5 20.96328.475 43.026

Moving distance of the third lens group L3 for focusing when the objectdistance is 0.45 m are shown in Table 3 below.

TABLE 3 Wide angle position Middle position Telephoto position 1.8102.109 3.149

Aspheric coefficients are shown in Table 4 below.

TABLE 4 Lens surface R K A4 A6 A8 A10 S20 −27.831 0.00000 7.44814E−054.32792E−07 0.00000 0.00000

With respect to the zoom lens according to Embodiment 1, FIG. 3 shows anaberration diagram when focused on an object at infinite distance at thewide angle position, FIG. 4 shows an aberration diagram when focused onan object at a minimum distance (0.45 m) at the wide angle position,FIG. 5 shows an aberration diagram when focused on an object at infinitedistance at the middle position, FIG. 6 shows an aberration diagram whenfocused on an object at a minimum distance (0.45 m) at the middleposition, FIG. 7 shows an aberration diagram when focused on an objectat infinite distance at the telephoto position, and FIG. 8 shows anaberration diagram when focused on an object at a minimum distance (0.45m) at the telephoto position.

FIGS. 3 to 8 show spherical aberration at a wavelength of about 656 nm(solid line), at a wavelength of about 588 nm (dashed line), at awavelength of about 486 nm (chain line), and at a wavelength of about436 nm (chain double-dashed line).

FIGS. 3 to 8 show astigmatism of sagittal rays (S1 to S4) and tangentialrays (T1 to T4) at each wavelength.

FIGS. 3 to 8 show distortion at a wavelength of about 588 nm (dashedline). In the zoom lens according to Embodiment 1, the aberrations arecorrected as shown in FIGS. 3 to 8.

Embodiment 2

FIG. 9 shows a zoom lens designed based on data according to Embodiment2. The zoom lens shown in FIG. 9 has the same constitution as the zoomlens shown in FIG. 1, and lens data of the zoom lens is listed in Table5 below. Table 5 is listed in the same manner as in Table 1.

TABLE 5 Lens surface R D nd vd S1 53.724 2.00 1.80518 25.46 S2 34.4356.30 1.69680 55.46 S3 328.432 D1 S4 78.396 1.20 1.71300 53.94 S5 10.9617.59 S6 −46.070 1.34 1.69680 55.46 S7 29.175 0.12 S8 19.296 4.15 1.8051825.46 S9 75.176 D2 S10 50.691 1.86 1.65160 58.40 S11 −41.933 D3 S12 stop0.10 S13 12.516 3.39 1.48749 70.44 S14 −43.926 0.60 1.84666 23.78 S1561.068 3.76 S16 −196.434 1.80 1.70154 41.15 S17 −18.007 0.55 1.6516058.40 S18 45.182 D4 S19 28.582 3.30 1.58313 59.46 S20 −28.733 1.73 S21−25.040 2.07 1.80611 40.73 S22 −119.822 D5 S23 plane 2.24 1.51633 64.14S24 plane 0.10

Variable distances during zooming from the wide angle position to thetelephoto position are shown in Table 6 below.

TABLE 6 Wide angle Variable position Middle Telephoto distance (f =18.55) position (f = 28.0) position (f = 53.4) D1 0.850 9.422 23.523 D215.365 9.027 2.340 D3 4.147 4.555 5.816 D4 4.519 3.284 1.894 D5 20.76428.285 42.896

Moving distance of the third lens group L3 for focusing when the objectdistance is 0.45 m are shown in Table 7 below.

TABLE 7 Wide angle position Middle position Telephoto position 1.7952.107 3.160

Aspheric coefficients are shown in Table 8 below.

TABLE 8 Lens surface R K A4 A6 A8 A10 S20 −28.733 0.00000 8.59850E−053.95336E−07 0.00000 0.00000

With respect to the zoom lens according to Embodiment 2, FIG. 10 showsan aberration diagram when focused on an object at infinite distance atthe wide angle position, FIG. 11 shows an aberration diagram whenfocused on an object at a minimum distance (0.45 m) at the wide angleposition, FIG. 12 shows an aberration diagram when focused on an objectat infinite distance at the middle position, FIG. 13 shows an aberrationdiagram when focused on an object at a minimum distance (0.45 m) at themiddle position, FIG. 14 shows an aberration diagram when focused on anobject at infinite distance at the telephoto position, and FIG. 15 showsan aberration diagram when focused on an object at a minimum distance(0.45 m) at the telephoto position. FIGS. 10 to 15 are illustrated inthe same manner as FIGS. 3 to 8.

Embodiment 3

FIG. 16 shows a zoom lens designed based on data according to Embodiment3. The zoom lens shown in FIG. 16 has the same constitution as the zoomlens shown in FIG. 1, and lens data of the zoom lens is listed in Table9 below.

TABLE 9 Lens surface R D nd vd S1 66.259 2.00 1.80518 25.43 S2 39.8094.93 1.69680 55.53 S3 860.809 D1 S4 79.706 1.20 1.71300 53.87 S5 10.6456.40 S6 −51.940 1.10 1.67790 55.34 S7 27.617 0.19 S8 18.534 4.41 1.8051825.43 S9 82.504 D2 S10 132.150 1.80 1.67790 55.34 S11 −37.919 D3 S12stop 0.10 S13 13.288 3.43 1.51633 64.14 S14 −32.398 0.68 1.80518 25.43S15 59.635 3.27 S16 122.239 2.59 1.80610 40.93 S17 −18.348 0.55 1.7432049.34 S18 50.261 D4 S19 30.419 3.32 1.58313 59.39 S20 −27.758 1.69 S21−24.094 1.56 1.79952 42.22 S22 −402.408 D5 S23 plane 2.24 1.51633 64.14S24 plane 0.10

Variable distances during zooming from the wide angle position to thetelephoto position are shown in Table 10 below.

TABLE 10 Wide angle Variable position Middle Telephoto distance (f =18.55) position (f = 28.0) position (f = 53.4) D1 1.847 12.000 25.328 D215.874 8.822 2.026 D3 2.510 2.769 3.820 D4 5.708 4.541 3.362 D5 21.07029.455 45.509

Moving distance of the third lens group L3 for focusing when the objectdistance is 0.45 m are shown in Table 11 below.

TABLE 11 Wide angle position Middle position Telephoto position 1.8172.270 3.319

Aspheric coefficients are shown in Table 12 below.

TABLE 12 Lens surface R K A4 A6 A8 A10 S20 −27.758 0.00000 7.56671E−053.60183E−07 0.00000 0.00000

With respect to the zoom lens according to Embodiment 3, FIG. 17 showsan aberration diagram when focused on an object at infinite distance atthe wide angle position, FIG. 18 shows an aberration diagram whenfocused on an object at a minimum distance (0.45 m) at the wide angleposition, FIG. 19 shows an aberration diagram when focused on an objectat infinite distance at the middle position, FIG. 20 shows an aberrationdiagram when focused on an object at a minimum distance (0.45 m) at themiddle position, FIG. 21 shows an aberration diagram when focused on anobject at infinite distance at the telephoto position, and FIG. 22 showsan aberration diagram when focused on an object at a minimum distance(0.45 m) at the telephoto position. FIGS. 17 to 22 are illustrated inthe same manner as FIGS. 3 to 8.

Embodiment 4

FIG. 23 shows a zoom lens designed based on data according to Embodiment4. A zoom lens according to Embodiment 4, which is different from thezoom lens shown in FIG. 1, includes: a first lens group L1 that includesa doublet lens having a negative meniscus lens 1 with a convex surfacetowards the object side and a positive lens 2 and a positive lens 3; asecond lens group L2 that includes a negative meniscus lens 4 with aconvex surface towards the object side, a biconcave lens 5, a positivelens 6 with a convex surface towards the object side, and a negativelens 7; a third lens group L3 that includes a doublet lens having anegative lens 8 and a positive lens 9; a fourth lens group L4 thatincludes a doublet lens having a positive lens 10 and a negative lens 11and a doublet lens having a negative lens 12 and a positive lens 13; anda fifth lens group L5 that includes a positive lens 14, a doublet lenshaving a positive lens 15 and a negative lens 16, and a positive lens17. A stop S may be disposed between the second lens group L2 and thethird lens group L3, and an optical filter such as LPF may be disposedbetween the fifth lens group L5 and the image plane IP.

In the zoom lens according to Embodiment 4, each of the first to fifthlens groups L1 to L5 may be shifted towards the object side such thatthe axial distance between the first lens group L1 and the second lensgroup L2 increases and the axial distance between the second lens groupL2 and the third lens group L3 decreases during zooming from the wideangle position to the telephoto position as shown in FIG. 23. Inaddition, the stop S may be integrally shifted with the fourth lensgroup L4 during zooming. In addition, as shown with an arrow F of FIG.23, the third lens group L3 may be shifted towards the image side I toperform a focusing at the minimum distance. The doublet lens includingthe negative lens 12 and the positive lens 13 of the fourth lens groupL4 may be shifted in a direction perpendicular to the optical axis tocorrect image shake caused by hand shaking.

Lens data for designing the zoom lens according to Embodiment 4 arelisted in Table 13 below. Table 13 is listed in the same manner as inTable 1.

TABLE 13 Lens surface R D nd vd S1 147.109 2.00 1.80518 25.43 S2 70.6947.37 1.49700 81.55 S3 −371.921 0.12 S4 60.382 6.07 1.63854 55.38 S5250.512 D1 S6 500.000 1.59 1.83481 42.71 S7 15.515 5.87 S8 −29.927 1.331.80400 46.57 S9 168.198 0.18 S10 33.189 5.42 1.84666 23.78 S11 −25.1220.53 S12 −20.683 1.21 1.83481 42.71 S13 272.781 D2 S14 stop 0.50 S1552.106 0.85 1.80000 29.84 S16 34.027 3.45 1.62299 58.17 S17 −30.895 8.26S18 17.757 4.07 1.48749 70.24 S19 −61.908 1.13 1.84666 23.78 S20 81.3733.11 S21 248.488 1.10 1.80610 40.93 S22 16.149 2.20 1.80518 25.43 S2325.026 D4 S24 50.994 5.10 1.67790 55.34 S25 −40.340 0.29 S26 43.521 4.031.49700 81.55 S27 −139.478 1.66 1.83481 42.71 S28 22.547 1.53 S29 26.2435.65 1.63980 34.47 S30 109.903 D5 S31 plane 2.24 S32 plane 0.60

Variable distances during zooming from the wide angle position to thetelephoto position are shown in Table 14 below.

TABLE 14 Wide angle Variable position Middle Telephoto distance (f =18.55) position (f = 69.0) position (f = 194.3) D1 2.460 31.855 55.017D2 26.958 9.612 1.670 D3 14.437 2.316 2.305 D4 18.581 52.002 65.944

Moving distances of the third lens group L3 for focusing when the objectdistance is 0.45 m are shown in Table 15 below.

TABLE 15 Wide angle position Middle position Telephoto position 1.5002.446 7.704

Aspheric coefficients are shown in Table 16 below.

TABLE 16 Lens surface R K A4 A6 A8 A10 S6 500.000 0.00000 1.97889E−063.56674E−09 3.05132E−11 0.00000E+00 S17 −30.895 0.00000 8.54454E−060.00000E+00 0.00000E+00 0.00000E+00 S21 248.488 0.00000 7.53970E−06−2.04757E−08 0.00000E+00 0.00000E+00 S24 50.994 0.00000 −1.24767E−05−8.80785E−09 0.00000E+00 0.00000E+00

With respect to the zoom lens according to Embodiment 4, FIG. 24 showsan aberration diagram when focused on an object at infinite distance atthe wide angle position, FIG. 25 shows an aberration diagram whenfocused on an object at a minimum distance (0.45 m) at the wide angleposition, FIG. 26 shows an aberration diagram when focused on an objectat infinite distance at the middle position, FIG. 27 shows an aberrationdiagram when focused on an object at a minimum distance (0.45 m) at themiddle position, FIG. 28 shows an aberration diagram when focused on anobject at infinite distance at the telephoto position, and FIG. 29 showsan aberration diagram when focused on an object at a minimum distance(0.45 m) at the telephoto position. FIGS. 25 to 29 are illustrated inthe same manner as FIGS. 3 to 8.

According to the following data, it can be seen that the zoom lensaccording to embodiments of the invention satisfies Formulae 1 to 19.

TABLE 17 Formula Embodiment 1 Embodiment 2 Embodiment 3 Embodiment 4f₃/f_(rt) 0.689 0.724 1.068 0.283 |f₃/f₂| 2.333 2.387 2.748 2.476 |1 −β_(3t) ² × β _(× t) ²| 3.700 3.700 3.686 7.503 1 − β_(3w) ² × β _(× w)²/ 22.198 15.352 3.332 21.090 1 − β_(3t) ² × β _(× t) ² |f₁/(f_(w) ×f_(t))^(1/2)| 3.209 3.210 3.636 1.585 |f₂/(f_(w) × f_(t))^(1/2)| 0.4700.473 0.502 0.226 |f_(rt)/(f_(w) × f_(t))^(1/2)| 1.592 1.557 1.291 1.976

As described above, the zoom lens according to the invention has highzoom magnification and excellent optical performance from the wide angleposition to the telephoto position. In addition the zoom lens hasexcellent focusing performance at the minimum distance. Furthermore, thezoom lens may be suitably applied to an auto-focusing control by bokehsensing of the imaging device.

While the invention has been particularly shown and described withreference to exemplary embodiments thereof, it will be understood bythose of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the invention as defined by the following claims.

1. A zoom lens comprising: a first lens group having a positive refractive power, a second lens group having a negative refractive power, and an additional lens grouping having a positive refractive power, which are sequentially arranged from an object side, wherein the additional lens grouping comprises a third lens group having a positive refractive power, wherein the third lens group is shifted towards an image side to perform focusing at a minimum distance, and wherein when an effective focal length of the third lens group refers to f₃[mm], and an effective focal length of the additional lens grouping at the telephoto position refers to f_(rt)[mm], and an effective focal length of the second lens group refers to f₂[mm], the zoom lens satisfies the following formulae: Formulae 0.1<f ₃ /f _(rt)<2.0, 1.5<|f ₃ /f ₂|<4.0.
 2. The zoom lens of claim 1, wherein a distance between the first lens group and the second lens group increases and a distance between the second lens group and the third lens group decreases during zooming from the wide angle position to the telephoto position.
 3. The zoom lens of claim 1, wherein the third lens group comprises one piece of positive lens.
 4. The zoom lens of claim 1, wherein when a transverse magnification of the third lens group when focused on an object at infinite distance at the telephoto position refers to β_(3t), and a transverse magnification of a lens group that is disposed closer to the image side than the third lens group and focused on an object at infinite distance at the telephoto position refers to β_(xt), the zoom lens satisfies the following formula: Formula |(1−β_(3t) ²)×β_(xt) ²|>2.0.
 5. The zoom lens of claim 1, wherein when a transverse magnification of the third lens group when focused on an object at infinite distance at the wide angle position refers to β_(3w), and a transverse magnification of a lens group that is disposed closer to the image side than the third lens group and focused on an object at infinite distance at the telephoto position refers to β_(xw), the zoom lens satisfies the following formula: Formula {(1−β_(3w) ²)×β_(xw) ²}/{(1−β_(3t) ²)×β_(xt) ²}>0.
 6. The zoom lens of claim 1, wherein when an effective focal length of the first lens group refers to f₁[mm], an effective focal length of the second lens group refers to f₂[mm], a total focal length of the zoom lens at the wide angle position refers to f_(w)[mm], and a total focal length of the zoom lens at the telephoto position refers to f_(t)[mm], the zoom lens satisfies the following formulae: Formulae 1.0<|f ₁/(f _(w) ×f _(t))^(1/2)|<5.05, 0.1<|f ₂/(f _(w) ×f _(t))^(1/2)|<1.0, 0.5<|f _(rt)/(f _(w) ×f _(t))^(1/2)|<3.0.
 7. The zoom lens of claim 1, wherein the first lens group comprises a negative meniscus lens with a convex surface towards the object side and a positive lens.
 8. The zoom lens of claim 1, wherein the second lens group comprises a negative meniscus lens with a convex surface towards the object side, a biconcave lens, and a positive lens with a convex surface towards the object side.
 9. The zoom lens of claim 1, wherein the third lens group comprises a biconvex lens.
 10. The zoom lens of claim 1, wherein the additional lens grouping further comprises a fourth lens group, and the fourth lens group comprises a doublet lens having a positive lens and a negative lens and a doublet lens having a positive lens and a negative lens.
 11. The zoom lens of claim 1, wherein the additional lens grouping further comprises a fifth lens group, and the fifth lens group comprises a positive lens and a negative lens.
 12. The zoom lens of claim 1, wherein the first lens group comprises a doublet lens having a negative meniscus lens with a convex surface towards the object side and a positive lens and a positive lens.
 13. The zoom lens of claim 1, wherein the third lens group comprises a doublet lens having a negative lens and a positive lens.
 14. The zoom lens of claim 1, wherein the additional lens grouping further comprises a fifth lens group, and the fifth lens group comprises a positive lens, a doublet lens having a positive lens and a negative lens, and a positive lens.
 15. A zoom lens comprising: a first lens group having a positive refractive power, a second lens group having a negative refractive power, and an additional lens grouping having a positive refractive power, which are sequentially arranged from an object side, wherein the additional lens grouping comprises a third lens group having a positive refractive power, wherein the additional lens grouping further comprises a fourth lens group and a fifth lens group which are sequentially disposed between the third lens group and an image side, wherein the distance between the fourth lens group and the fifth lens group varies during zooming, and wherein when an effective focal length of the third lens group refers to f₃[mm], and an effective focal length of the additional lens grouping at the telephoto position refers to f_(rt)[mm], and an effective focal length of the second lens group refers to f₂[mm], the zoom lens satisfies the following formulae: Formulae 0.1<f ₃ /f _(rt)<2.0, 1.5<|f ₃ /f ₂|<4.0.
 16. A photographing apparatus comprising: a zoom lens; and an imaging device that picks up an image formed by the zoom lens, wherein the zoom lens comprises a first lens group having a positive refractive power, a second lens group having a negative refractive power, and an additional lens grouping having a positive refractive power, which are sequentially arranged from an object side, wherein the additional lens grouping comprises a third lens group having a positive refractive power, wherein the third lens group is shifted towards an image side to perform focusing at a minimum distance, and wherein when an effective focal length of the third lens group refers to f₃[mm], and an effective focal length of the additional lens grouping at the telephoto position refers to f_(rt)[mm], and an effective focal length of the second lens group refers to f₂[mm], the zoom lens satisfies the following formulae: Formulae 0.1<f ₃ /f _(rt)<2.0, 1.5<|f ₃ /f ₂|<4.0.
 17. A photographing apparatus comprising: a zoom lens; and an imaging device that picks up an image formed by the zoom lens, wherein the zoom lens comprises a first lens group having a positive refractive power, a second lens group having a negative refractive power, and an additional lens grouping having a positive refractive power, which are sequentially arranged from an object side, wherein the additional lens grouping comprises a third lens group having a positive refractive power, wherein the additional lens grouping further comprises a fourth lens group and a fifth lens group which are sequentially disposed between the third lens group and an image side, wherein the distance between the fourth lens group and the fifth lens group varies during zooming, and wherein when an effective focal length of the third lens group refers to f₃[mm], and an effective focal length of the additional lens grouping at the telephoto position refers to f_(rt)[mm], and an effective focal length of the second lens group refers to f₂[mm], the zoom lens satisfies the following formulae: Formulae 0.1<f ₃ /f _(rt)<2.0, 1.5<|f ₃ /f ₂|<4.0. 